1. Field of the Invention
The present invention relates to a chip-type noise filter for eliminating high-frequency noise entering a signal line of electronic equipment, a manufacturing method thereof, and a semiconductor package using the chip-type noise filter.
2. Description of Related Art
In the recent years, to meet a market need for high-speed and large-scale information communication by optical communication and radio communication, the trend in the operating frequency and signal frequency of electronic equipment used for these communications is toward higher speeds from year to year.
In particular, the frequency of electric signals of electronic equipment used for high-speed optical communication and radio communication becomes high-speed up to a frequency band of not less than 10 GHz, which is called quasi-millimeter wave and millimeter wave. The problem of noise becomes pronounced as a problem common to equipment handling such frequencies.
When the frequency of an electric signal reaches the regions of quasi-millimeter wave and millimeter wave, it can be considered that an electric signal passing through a signal line is handled as an electromagnetic wave, and the electromagnetic wave propagates along the signal line thereby to transfer the electric signal.
Such an electric signal as an electromagnetic wave is susceptible to radiation into space at, for example, discontinuous surfaces, bent portions, etc. of a signal line, and in some cases, it may cause radiation noise.
This radiation noise is reflected in multiple at the inside of the casing of electronic equipment, and then enters other signal line as noise, thus causing the problem of noise, which is termed “crosstalk.”
As a component for eliminating so-called conduction noise so entered into a signal line, there has been manufactured a small chip-type noise filter, which is used by soldering on a substrate.
This type of filter configures an equivalent circuit consisting of parts L1, L2 and C, as shown in FIG. 4, and functions as a so-called low-pass filter, which cuts high frequencies and passes low frequencies.
A conventional chip-type noise filter employs ceramics as a dielectric, and it is manufactured in the following manner that: after forming a ceramics green sheet having a predetermined thickness, a circuit member and an electrode member are arranged thereon by screen printing or the like, and as required, a plurality of the green sheets are laminated and adhered to each other, followed by firing for integration (Japanese unexamined Patent Publication No. 2000-21640).
As a noise filter usable in a high-frequency band including quasi-millimeter wave and millimeter wave, there is disclosed a chip-type noise filter having a signal line consisting of a conductor in the state of being adhered to the surface of a composite material in which soft magnetic material powder is dispersed and mixed in a matrix such as rubber or plastic (Japanese unexamined Patent Publication No. 2002-171104).
However, the frequency of noise, which can be eliminated by the filter as disclosed in Japanese unexamined Patent Publication No. 2000-21640, is approximately 3 GHz in maximum, thus failing to eliminate noise of quasi-millimeter wave and millimeter. In addition, the manufacturing method thereof is expensive in processing cost, and there is a problem in reducing the cost of parts.
On the other hand, the filter as disclosed in Japanese unexamined Patent Publication No. 2002-171104 can eliminate the noise of quasi-millimeter wave and millimeter wave. However, since rubber or plastic etc. is used as a matrix, there is the problem that, depending on the manufacturing conditions and operating conditions of electronic equipment, outgassing occurs at the time of temperature rise, thereby to corrode an electric circuit and a signal line in the surroundings, and also cause deterioration of characteristics.
In particular, the application of this filter to portions for which high airtight is required, such as the inside of a semiconductor package, suffers from the following problem. At the time of temperature rise in the manufacturing step of the semiconductor package and under operating environment, outgassing occurs to deteriorate the characteristics of a semiconductor device and corrode a peripheral signal line, thus deteriorating transmission characteristics.